[BUG] Use up to date Chromium version in device User-Agents

[mxschmitt]

Context: https://playwright.slack.com/archives/CSUHZPVLM/p1613146477170900

Actual: Currently if someone will use a Pixel 2, he will get Chrome 75
Expected: He should get an up to date version or the from the current roll

drive-by: maybe add also the latest iPhones.